Active-oxygen compounds such as e.g. - compounds which split off (inorganic or organic) hydrogen peroxide or inorganic or organic peracids are used as bleaching agents, especially in detergents, bleaching and cleaning agents. It is however known that some active-oxygen compounds tend to cake if stored for a fairly long time. The product, stored in sacks, containers or silos, forms clumps and hardens in such instances, which makes it harder or even impossible to handle, e.g. to transport or measure.
As is known, sodium percarbonate exhibits a particularly strong tendency to clump and cake. When selecting an active-oxygen compound for an application, this property is considered, along with its active-oxygen stability, which is less than that of sodium perborate hydrates. For this reason, sodium percarbonate is less widely used as bleaching component. While many methods have been suggested for stabilizing sodium percarbonate, it has not yet been possible to solve the problem of caking in a satisfactory manner. Even sodium percarbonate, prepared and stabilized according to various methods, exhibits a more or less strong tendency to cake.
Published German Patent Specification DE-OS No. 27 00 797 (corresponding to U.S. Pat. No. 4,179,394) teaches a method of improving the storage life, especially the silo storage life, of oxygen-releasing compounds such as e.g. sodium percarbonate. The method consists of granulating the oxygen-releasing compound in the presence of water together with sodium tripolyphosphate and/or sodium pyrophosphate, optionally with the addition of other detergent builders and auxiliary granulating agents which have a stabilizing action on active-oxygen such as e.g. water glass, magnesium phosphate or hexametaphosphate. Then, the granulates, which have formed, are dried. The oxygen-releasing compound and the phosphate are granulated in a weight ratio of 1:0.1 to 1:1, preferably 1:0.2 to 1:0.4. Phosphonic acids are named without a more specific characterization among the detergent components which can be usefully worked into the granulates. There are no suggestions as to which phosphonic acids are intended, in what amount they are to be added and what effect they have.
One disadvantage of this known method is the relatively expensive granulating method, which follows the actual preparation of the active-oxygen compound as a completely separate method step. In addition, the granulates produced in this manner exhibit a lower effective active-oxygen content and may contain components which interfere with use in a broad range of formulations. The manufacturer of active-oxygen compounds therefore attempts to minimize the use of auxiliary agents and to minimize their concentration as much as possible in order to obtain essential properties such as a low tendency to cake.
It is known that phosphonic acid compounds capable of chelate complex formation with heavy metals which break down active-oxygen compounds are used for stabilizing active-oxygen compounds during their preparation or formulation to detergents and cleaning agents. Thus, published German Patent Specification DE-OS No. 26 22 458 (corresponding to U.S. Pat. No. 4,117,087) teaches the use of hydrogen peroxide containing 1-hydroxyethane-1,1-diphosphonic acid for preparing sodium percarbonate in a wet method. However, a percarbonate which greatly caked was obtained in the reworking of this method. Even an addition of the phosphonic acid cited above to the soda additive solution of the (sodium percarbonate) method of preparation - according to the disclosure of German Patent DE-PS No. 28 00 760 (corresponding to British Patent 2,011,874) did not result in any appreciable reduction of the caking tendency. None of the known methods are concerned with the use of such phosphonic acid compounds for reducing caking, nor are these compounds brought in contact as an aqueous solution with the previously-formed active-oxygen compounds as in the present invention as described below.